88 lines
1.9 KiB
Go
88 lines
1.9 KiB
Go
// Copyright 2010 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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// The original C code and the comment below are from
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// FreeBSD's /usr/src/lib/msun/src/e_remainder.c and came
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// with this notice. The go code is a simplified version of
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// the original C.
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//
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// ====================================================
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// Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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//
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// Developed at SunPro, a Sun Microsystems, Inc. business.
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// Permission to use, copy, modify, and distribute this
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// software is freely granted, provided that this notice
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// is preserved.
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// ====================================================
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//
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// __ieee754_remainder(x,y)
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// Return :
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// returns x REM y = x - [x/y]*y as if in infinite
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// precision arithmetic, where [x/y] is the (infinite bit)
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// integer nearest x/y (in half way cases, choose the even one).
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// Method :
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// Based on Mod() returning x - [x/y]chopped * y exactly.
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// Remainder returns the IEEE 754 floating-point remainder of x/y.
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//
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// Special cases are:
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// Remainder(±Inf, y) = NaN
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// Remainder(NaN, y) = NaN
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// Remainder(x, 0) = NaN
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// Remainder(x, ±Inf) = x
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// Remainder(x, NaN) = NaN
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func Remainder(x, y float64) float64 {
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return remainder(x, y)
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}
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func remainder(x, y float64) float64 {
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const (
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Tiny = 4.45014771701440276618e-308 // 0x0020000000000000
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HalfMax = MaxFloat64 / 2
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)
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// special cases
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switch {
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case IsNaN(x) || IsNaN(y) || IsInf(x, 0) || y == 0:
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return NaN()
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case IsInf(y, 0):
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return x
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}
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sign := false
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if x < 0 {
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x = -x
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sign = true
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}
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if y < 0 {
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y = -y
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}
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if x == y {
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return 0
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}
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if y <= HalfMax {
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x = Mod(x, y+y) // now x < 2y
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}
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if y < Tiny {
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if x+x > y {
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x -= y
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if x+x >= y {
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x -= y
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}
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}
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} else {
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yHalf := 0.5 * y
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if x > yHalf {
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x -= y
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if x >= yHalf {
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x -= y
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}
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}
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}
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if sign {
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x = -x
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}
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return x
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}
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